In the semiconductor manufacturing industry, gas cabinets are used to supply high purity process gases used in production. An example of such a process gas is silane, which is used at the processing location, also known as the tool location, in processes such as sputtering and sputter etching. Silane, like many process gases, is highly toxic and it is of the utmost importance for the safety and health of the workers that the flow of these toxic gases be tightly and safely controlled. The equipment and methods of controlling the functions of the gas cabinets supplying the process gas are therefore of great significance in this industry.
There are several problems with prior gas supply systems. In prior systems, the changing of a supply of toxic gas is accomplished with the use of semi-automatic means to purge the toxic process gas from the gas feed lines. Toxic gas first is removed from the feed line leading from the tank, and then a purging gas such as nitrogen is fed into the feed line to dilute the toxic gas in the feed line. This cycle is repeated a number of times by the operator. Then, the original tank is disconnected from the feed line, and a new tank is connected in its place. Next, the purge gas is removed from the feed line and replaced with the process gas from the new tank in a procedure similar to that of the first purge.
The number of times each purge cycle is repeated is fixed, as if the time duration of each cycle. The problem is that different types of process gas require different numbers and times of purge cycles, as well as different pressures. Because the cycle durations and numbers of cycles which are right for one gas, may be dangerous when used for another, and because equipment can be damaged due to incorrect settings, the inflexibility of prior equipment has detracted from its safety and cost-effectiveness.
Another problem with such prior equipment and methods is that if the cycle times and/or the number of purge cycles is larger than necessary, the process of changing the supply tank is more time-consuming and expensive than it need be.
Another problem is that the gas supply system usually has one or more gas filters which become contaminated and must be replaced from time to time. In prior systems, in order to purge the gas lines, purge gas is sent through the entire gas distribution system to the tool location. Then the filter is replaced, and the entire line is re-filled with process gas. This uses relatively large amounts of expensive, purified purge gas and process gas, and is very time-consuming. The use of bypass lines to reduce the conduit length has been suggested, but not how to use the same.
Another problem with such prior gas supply systems is that it is a time-consuming and inefficient process to establish set points for alarms and safety devices. Setpoints are e.g., the gas pressures at which alarms are activated due to pressures which are too low or too high. In an installation including many different gas cabinets, with past equipment it has been necessary to change the setpoint of each cabinet manually--a time--consuming, expensive procedure.
In some prior systems, a separate control panel for each cabinet is located in a single control room remote from the gas cabinets controlled from the room. This requires a great deal of costly hardware and building construction, as well as still being relatively slow to use in establishing setpoints.
A further problem with prior equipment and methods is that a substantial portion of the record-keeping is manual, tedious and costly. Moreover, it is not reliable and may not be adequate to show that the various cycling procedures and setpoints were maintained safely, in accordance with OSHA standards, in case of an accident.